Animals constantly process and respond to environmental cues. Leeches are well suited for studies of sensorimotor integrations because one can monitor their neuronal activity during ongoing behavior and work out detailed connectivity for the neuronal circuits. Moreover, leeches appear to use the same kind of population codes as are found in other sensory- motor systems. To determine the nature of the vector calculations used by the leech CNS, voltage sensitive-dyes will identify interneurons and characterize how inhibitor connections among motor neurons influence motor control; all connections will be confirmed electrophysiologically. Electromyography will be used to measure bend amplitude and direction in response to localized touches delivered to the leech body wall. Then the bending response will be examined without inhibition in the circuit. Computational models of the network will be used to test different population coding strategies and the effects of removing inhibition. Collectively, the results of the experiments and modeling should identify the type of code the leech nervous system uses to process sensory input to direct behavioral output and will show the function of inhibition in forming the vector code.